Single-, dual- or multiple-stage ferrofluid seals are usefully employed for forming one or more ferrofluid O-rings about a shaft element, to provide for sealing about the shaft element. Ferrofluid seals are employed with shafts having moderate speed rotation and are useful for sealing in bearing lubricants, in order to prevent the bearing lubricants from reaching areas that must be free of contamination. While such ferrofluid seals can withstand typically a gas-pressure difference of about 3 to 5 psi per ferrofluid stage, such ferrofluid seals are generally incapable of withstanding liquid pressure; for example, a magnetic fluid pressure, and even low pressure, during dynamic operations; that is, when the shaft is being rotated. Such liquid-pressure situations may arise, for example, when a bearing lubricant reservoir is attached for replenishment of the bearing fluid, or when a reservoir is combined with circulation through a cooler, in order to maintain the desired bearing temperature during dynamic operation of the shaft.
Under dynamic operating conditions, the ferrofluid, which includes ferrolubricants which perform the functions of providing a fluid film, as well as a lubricating film for a ferrofluid bearing, tends to move longitudinally outwardly, due to the rise in temperature under the operating conditions, and expansion of the ferrofluid, by virtue of the heat generated by the shearing forces on the ferrofluid and the differential expansion of the component parts of the bearing.
Bifluid, hydrodynamic bearing systems have been described, for example, in U.S. Pat. No. 3,439,961 in which scavenger grooves are employed, to impel the bearing fluid toward the axial center of the bearing cavity, so as to reduce any leakage of the bearing fluid under load or dynamic conditions. This patent also provides a ferromagnetic fluid as a bearing lubricant, wherein the bearing lubricant is magnetized and retained in position not only through the magnetic field, but through the use of nonwetting TEFLON material at each end of the bearing cavity. In addition, U.S. Pat. No. 3,891,282 discloses an assembly, wherein use is made of spiralling channels which urge a lubricant into the bearing gap of a lubricating bearing assembly, where the shaft of the bearing assembly is sealed by a magnetic seal.
It is desirable to provide a composite ferrofluid-seal, fluid-film bearing, either radial, thrust or a combination of radial and thrust, apparatus of simple design and construction and which provides an effective means to retain the ferrolubricant employed in the bearing cavity, particularly under dynamic operating conditions.